I think a lot of that depends on the map. I personally love building into the side of a mountain, so that it conforms with the landscape, while looking modern and awesome. It also keeps the place decently hidden.
I wonder what types of players build above ground vs below ground. I'm a mat collecting freak. I love going exploring, hunting for all the mats I can get. I usually have serious stockpiles. But at the same time, I love redoing the landscape to fit my needs. I once hollowed out a mountain to make an indoor aboritum, as well as adding a few lakes and a dam.